Field of the Invention
The present invention relates to a motor control device for driving a motor (rotating machine) by an electric power converter which outputs desired electric power by means of repetitions of a turn-on operation and a turn-off operation in two arms constituted of switching devices, and more particularly to a motor control device using an electric power converter for driving switching devices utilizing a pulse width modulation (Pulse-Width Modulation, hereinafter referred to as a “PWM,” for brevity).
Description of the Related Art
In the field of a motor (the same as a rotating machine, hereinafter in a similar fashion) control, development of technologies is in progress in estimating mechanical state-values such as a position and speed of the motor, and torque thereof or the like from electrical state-values of electric voltages, currents and the like. In these technical areas, it is important as a matter of course to accurately acquire the electrical state-values of electric voltages, currents and the like having been the source without being influenced by the disturbance.
In particular, as disturbance which exerts bad influence on voltage acquisition, a dead-time disturbance voltage generated by an electric power converter can be named. In what follows, the explanation will be made for the dead-time disturbance voltage.
In the electric power converter, power device elements of two arms constituting of an electric power conversion means provided in an output stage perform switching operations based on voltage instructions to generate alternating-current voltages, which are outputted into an alternating-current load(s); as an object to prevent short-circuiting breakdown due to simultaneous conduction of the power device elements of two arms, a period is set in which the power device elements of two arms are controlled to be put in turn-off operation states at the same time. This period is referred to as “dead time”; due to the dead time, an error occurs between a voltage instruction in which the electric power conversion means receives, and a voltage in which the electric power conversion means actually outputs to a load based on the voltage instruction.
It is known that error voltages originating in the dead time are determined from a dead-time period Td, a carrier frequency fc and a direct-current voltage Vdc, and take such waveforms shown by the solid lines in FIG. 1.
To be specific, voltage in the shape of pulses each having a slight area of Td×Vdc is synchronized with each of the polarities of a three-phase output current [i] (a set of symbols [ ] designates that the quantity in the square brackets is a vector, hereinafter in a similar fashion), and is such a disturbance voltage where the pulses rise for a number of fc times per half a period of the [i].
From the solid-line waveforms in FIG. 1, it can be understood that, as expressed by the following Equation (1) when consideration is given to a time average, these dead-time disturbance voltages have a reversed polarity to an individual polarity of the three-phase output current [i] from an electric power conversion means, and are equivalent to a voltage in the shape of a three-phase rectangular wave such that the amplitude is VTd=Td×fc×Vdc.[vTd]=−sgn[i]×VTd  (1)
When Equation (1) is depicted, which results in such a waveform of the broken line (indicated by the symbol “Q”) in FIG. 1.
As it is clear from the waveform, it can be said that the dead-time disturbance voltages has rises or descents for six times per one period at motor's electrical angle in a sum total of three phases, and that disturbance vibrating with six-times order component at motor's electrical angle (hereinafter referred to as a “6f-component”) occurs with respect to torque in which the motor produces (hereinafter referred to as a “torque ripple”). Note that, the disturbance vibrating with six-times order component at motor's electrical angle is hereinafter referred to as as a “6f torque ripple.” Note also that, the solid-line curve indicated by the symbol “P” in the shape of a sinusoidal wave (sine wave) in FIG. 1 shows a phase-U current waveform.
When Equation (1) is based on, a negative-phase-sequence voltage as indicated in Equation (2) (namely, a voltage in the shape of a three-phase rectangular wave having the same polarity with the phase current, and the amplitude being VTd) is added in advance, in comparison with Equation (1), to each phase of voltage instructions to be inputted into the electric power converter, so that it becomes possible to compensate a disturbance voltage(s) originating in the dead time.[vTd]=sgn[i]×VTd  (2)
When Equation (2) is depicted, it takes such a waveform as the dotted line in FIG. 1 (indicated by the symbol “R”).
The technologies described above are publicly known technologies relating to generation of the dead-time disturbance voltages and their compensation (for example, refer to Sugimoto, Koyama, and Tamai [Authors], “Actualities of Theory and Design of AC Servo Systems,” 1990, pp. 54-57 and pp. 72-85, [then] Sogo Denshi Shuppan-sha, Tokyo).
However, in power device elements inside the electric power converter, there exist error factors such as response delays of a turn-on operation and a turn-off operation, and ON-voltage drops of the power device elements and diodes; and thus, it can be said that an error occurs between a dead-time period Td being set on a controller, and a dead-time period actually produced inside the electric power converter.
If it is possible to accurately measure error times such as these response delays of a turn-on operation and a turn-off operation, and ON-voltage drops of the power device elements and the diodes, it can be said that modification for those quantities is suitable to be performed; however, it is actually difficult to accurately measure those error times. For dealing therewith, as one of the methods to cope with delays occurring in these actual device elements, a technology is proposed in which a dead-time disturbance voltage is appropriately estimated, and a dead-time disturbance compensation-voltage is generated (for example, refer to Japanese Laid-Open Patent Publication No. 2004-64948).
In such a technology, it is possible to estimate a dead-time disturbance voltage associated with delays in the device elements based on observations of only electrical state-values; from the viewpoints of easiness and convenience, the technology is useful in estimating the dead-time disturbance voltage.